U.S. Pat. No. 4,050,374 for a Meter Setting Mechanism, issued Sep. 27, 1977 to Check, Jr. and assigned to the assignee of the present invention, discloses a mechanism for selecting postage values which are to be printed by a rotary postage meter. The drive shaft of the drum includes a plurality of selectable racks, each of which is slidably movable in engagement with a different pinion gear, connected to an associated print wheel within the drum, for selectively rotating the print wheel to dispose a printing element or font thereof at the outer periphery of the drum for printing purposes. The value selection mechanism includes a first stepper motor which is operable for selecting one of the racks, and a second stepper motor which is operable for actuating the selected rack for selectively rotating the desired printing element of the associated print wheel to the printing position thereof. An electronic control system (not shown) which is coupled to a keyboard for processing postage value entries made by an operator, selectively drives the respective stepper motors in response to keyboard entries.
U.S. Pat. No. 4,630,210 for a Microprocessor Controlled D.C. Motor For Controlling A Load, issued Dec. 16, 1986 to Salazar, et. al., and assigned and the assignee of the present invention, shows a conventional postage meter including a plurality of lengthwise translatable racks mounted in channels formed in the drive shaft of a rotatable postage printing drum. The drum includes a plurality of print wheels, which are mounted for rotation in the drum, and a like number of pinion gears connected on a one-for-one basis with the print wheel. And, each of the pinion gears is disposed, on a one for one basis, in meshing engagement with each of the rack gears, so that lengthwise translation of a rack gear results in rotation of the associated print wheel to a selected position thereof wherein a printing font at the periphery of the print wheel is located for printing purposes when the drum is rotated.
U.S. Pat. No. 4,649,814 for a Rotary Selector Device, issued Mar. 17, 1987 to Sette and assigned to the assignee of the present invention, shows a rotary value selection mechanism, of the type used for selecting and driving the respective translatable racks of the aforesaid U.S. Pat. No. 4,630,210, including a first annularly-shaped rack selection member having a pinion gear mounted therewithin and movable therewith for selectively engaging the racks as the first member is rotated, and including a second annularly-shaped print-wheel-font selection member which is disposed in meshing engagement with the pinion gear teeth for translating the selected rack to move the associated print wheel as the second member is rotated.
Value selection mechanisms of the aforesaid types have from time-to-time become physically damaged such that one or more rack gears have become disassociated from its associated print wheel driving gear, with the result that the print wheels may be rotated independently thereof. Whereupon, a postage value can be printed which is different from that which has been selected by the associated, translating, rack gear. Although the occurrence of such physical damages are immediately apparent to a postage meter user, meters have been known to be continued to be used despite such a malfunction condition, in order to wrongfully print postage values without a payment being made therefor. Of course, since postage meters are required to be physically inspected on a semi-annual basis, and more frequently when Postal Service inspectors through internal postage indicia inspection controls and accounting practices suspect that a postage meter is dispensing more postage than has currently been paid for, such physical damages have a short life span due to their inevitably early discovery. Nevertheless, any postage payment losses are rightfully of great concern to the Postal Service and to postage meter manufacturers. As a result, a series of experimental activities with postage meters have been conducted to determine the basic cause, if any, of disassociation of postage selecting racks and print wheels. And, it has been experimentally determined that the majority of the instances in which such disassociations occur are due to a sufficient force being exerted against the print wheel to separate the same from the drive train therefor. Accordingly:
an object of the invention is to provide means for preventing disassociation of the rack gear and associated print wheel;
another object is to provide means for weakening the drive train, between the rack and print wheel of a value setting mechanism, against a force exerted against the print wheel which tends to separate the print wheel from the drive train; and
another object is to provide rotary value selection and printing apparatus, which includes a rack gear slidably mounted on a shaft which is weakened against the exertion of a sufficient force against the print wheel to permit the shaft to bend in response to the force, with the result that the rack gear becomes jammed against slidable movement thereon.